The present invention relates to methods, systems and apparatus for conveying information from a base station to a terminal device in a wireless telecommunications system to control a reduced activity mode at the terminal device to conserve resources.
Third and fourth generation mobile telecommunication systems, such as those based on the 3GPP defined UMTS and Long Term Evolution (LTE) architecture are able to support more sophisticated services than simple voice and messaging services offered by previous generations of mobile telecommunication systems.
For example, with the improved radio interface and enhanced data rates provided by LTE systems, a user is able to enjoy high data rate applications such as mobile video streaming and mobile video conferencing that would previously only have been available via a fixed line data connection. The demand to deploy third and fourth generation networks is therefore strong and the coverage area of these networks, i.e. geographic locations where access to the networks is possible, is expected to increase rapidly.
The anticipated widespread deployment of third and fourth generation networks has led to the parallel development of a class of devices and applications which, rather than taking advantage of the high data rates available, instead take advantage of the robust radio interface and increasing ubiquity of the coverage area. Examples include so-called machine type communication (MTC) applications, which are typified by semi-autonomous or autonomous wireless communication devices (i.e. MTC devices) communicating small amounts of data on a relatively infrequent basis. Examples include so-called smart meters which, for example, are located in a customer's house and periodically transmit information back to a central MTC server data relating to the customers consumption of a utility such as gas, water, electricity and so on. Further information on characteristics of MTC-type devices can be found, for example, in the corresponding standards, such as ETSI TS 122 368 V10.530 (2011-07)/3GPP TS 22.368 version 10.5.0 Release 10) [1]. Some typical characteristics of MTC type terminal devices/MTC type data might include, for example, characteristics such as low mobility, high delay tolerance, small data transmissions, infrequent transmission and group-based features, policing and addressing.
Whilst it can be convenient for a terminal such as an MTC type terminal to take advantage of the wide coverage area provided by a third or fourth generation mobile telecommunication network there are at present disadvantages. Unlike a conventional third or fourth generation terminal device such as a smartphone, an MTC-type terminal is preferably relatively simple and inexpensive and able to operate on relatively low resources (e.g. low power consumption). The type of functions performed by the MTC-type terminal (e.g. collecting and reporting back data) do not require particularly complex processing to perform, and furthermore are typically not time-critical. However, third and fourth generation mobile telecommunication networks typically employ advanced data modulation techniques on the radio interface which can be power hungry and require more complex and expensive radio transceivers to implement. It is usually justified to include such complex transceivers in a smartphone as a smartphone will typically require a powerful processor to perform typical smartphone type functions. However, as indicated above, there is now a desire to use relatively inexpensive and less complex devices able to operate with low resource usage to communicate using LTE type networks.
Known techniques for lowering power consumption in LTE-type terminal devices include the discontinuous reception (DRX) mode and the microsleep mode. The DRX mode involves controlling a terminal device to enter an idle mode through Radio Resource Control (RRC) signalling. Drawbacks of the DRX mode include reconnection latency as the terminal device moves from idle mode back to connected mode as well as initiation delays and signalling overhead associated with the RRC signalling. These can mean DRX is an efficient mechanism for saving terminal device resources when the device is to be idle for relatively long periods, for example, for hundreds of milliseconds or longer, but the DRX mode is less efficient for controlling shorter duration periods of reduced terminal device activity. The microsleep mode involves a terminal device determining from a control region of a subframe that there is no user-plane data for the terminal device in the remainder of the subframe, and suspending decoding of the remainder of the subframe accordingly. The microsleep mode is thus applicable for timescales which are much shorter than the DRX mode (i.e. microsleep can be applied on a per subframe basis). Furthermore, there is no RRC signalling overhead associated with microsleep. However, the microsleep mode requires a terminal device to decode a control region of each subframe to determine whether to microsleep for the remainder of the subframe and this restricts the extent to which the terminal device can save power. For example, unlike the DRX mode, the microsleep mode cannot be used to configure a terminal device into a continuous reduced-activity state for a number of subframes.
In view of the above-identified drawbacks of existing schemes, there is therefore a need for alternative approaches for controlling a terminal device communicating with a base station to enter a reduced activity mode.